A conventional electrode arrangement found in water purification apparatus is shown in FIG. 9, in which a positive electrode 91 and a negative electrode 93 are cylindrical with circular cross sections extending continuously along their lengths. The highest current density 92 between the electrodes is found in a common plane that intersects the diameters of both of the electrodes 91, 93. The respective outer surfaces of the electrodes 91, 93 are closest to one another in the common plane, that is, along narrow, substantially linear peripheral surface areas of the cylindrical electrodes intersected by the common plane.
Because the current density is greatest over such a narrow and relatively small surface area of the cylindrical electrodes 91, 93, cylindrical electrodes are not efficient in electrolyzing salts such as bromides. Additionally, certain cylindrical electrodes such as graphite can experience erosion along these narrow surface areas, releasing graphite particles into the electrolyte where the particles may accumulate. Further, the erosion causes the distance between the “closest” peripheral surface areas of the electrodes to increase. As the distance between electrodes increases, greater voltage is required to maintain current flux.
FIG. 10 is another example of a conventional electrode arrangement in which a positive electrode 101 and a negative electrode 103 each have a square cross section extending continuously along their lengths. The parallel plane surfaces of the electrodes 101, 103 facing one another provide a greater total surface area for quasi equal paths of greatest current flow 102 than the narrow, substantially linear areas of the cylindrical electrodes 91, 93 of FIG. 9. However, a problem with this conventional arrangement shown in FIG. 10 is that the opposite side surfaces of the electrodes make relatively insignificant contributions to overall current flow because they are coplanar with one another and farther from one another than the facing surfaces of the electrodes 101, 103. Also, sufficient uniform electrolyte fluid flow and fluid flow distribution across the electrode surface, in the parallel plane geometry of FIG. 10, is difficult to achieve. To the extent that direct flow of sufficient velocity may be achieved between the electrodes 101, 103, another problem arises in that the fluid flow can lead to premature failure of the graphite lattice. Still another problem is that dislodge graphite particles may become an aesthetic issue if the electrolyte is transparent.
Another drawback of conventional electrode geometry arrangements is compliance with industry standards. For example, UL Standard 1081 requires that the inlet to outlet voltage differential of the electrode assembly be essentially zero volts. UL Standard 1081 28.4 provides that there shall be no voltage drop in the water in the cell of an electrolytic chlorinator as measured between the water inlet and outlet, nor shall there be a flow of current, either alternating or direct, in excess of 1 milliampere from the water to ground. When using conventional parallel plane geometry, the zero volt differential between inlet and outlet is difficult to achieve because the geometrical orientation of the graphite electrodes in relation to the fluid flow inlet and the outlet will vary the differential voltage between the inlet and outlet.